The measurement of ultraviolet transmission is useful in a myriad of applications for determining the amount of degradation caused by ultraviolet rays to fabrics and similar articles, to products contained within translucent packaging materials therefor, including pharmaceutical product bottles or containers and the like, and also for ascertaining the degree of ultraviolet protection to the skin afforded by clothing and protective creams, including so-called sun-screen formulations.
In the past, such measurements have been made by striking the sample with ultraviolet light and collecting the light transmitted through the sample with an integrating sphere as, for example, of the type described in U.S. Pat. No. 5,537,203 of the common assignee of the present invention. The light is either provided by a scanning monochrometor, or a scanning, monochrometor is used to analyze the light after it passes into the sphere.
Limitations in such prior techniques, at least for the specific purposes of the present invention, as above summarized, include the relatively slow, several minute measurement time required of such scanning monochrometors, and the substitution errors exhibited in the integrating sphere measurements due to the presence of the sample on the sphere during its transmission measurement and the absence of the sample during the required reference beam scan measurement. In addition, fluorescent effects in the sample, common with commercial fabrics and other materials, cannot be satisfactorily dealt with in such monochrometors, though partially compensatory optical filters have been used. The steady irradiation required, moreover, can itself affect the sample, indeed, changing it in the very process of measurement.
The present invention, on the other hand, admirably overcomes all of these prior limitations and disadvantages through the use of a pulsed white light (xenon) lamp inside an integrating sphere and the use of two separate diode array spectrograph channels, with light collected in a single direction after it passes through the sample, and with one channel monitoring the inside of the sphere, and the other channel viewing the light transmitted through the sample.